A pneumatic yarn splicing device is known by U.S. Pat. No. 4,263,775.
In splicing yarn ends of spun yarns by means of the pneumatic yarn splicing device, it is necessary to untwist both yarn ends for a predetermined length prior to splicing by means of a yarn end untwisting device. Such a yarn end untwisting device guides both yarn ends into individual nozzle holes and applys a pressurized fluid against each yarn end within the corresponding nozzle hole to open or loosen the component fibers of the yarn end. In such an yarn end untwisting operation, the quantity of the pressurized fluid jetted against the yarn ends and the direction of jetting the pressurized fluid have to be changed and adjusted appropriately corresponding to the characteristics of yarns, namely, the thickness and the length of the component fibers and the number of twist per unit length. The fine adjustment of the quantity and the jetting direction of the pressurized fluid is essential to achieve appropriate untwisting, whereas the simple adjustment of the quantity of the pressurized fluid by means of a valve is insufficient to achieve satisfactory untwisting.